1990 8 HP Johson J8RESR

[bbx2]

Can some one tell me what the idle setting (am getting all the way from 1 1/2 to 5 turns out on internet) also how do you go about finding the correct setting for the carb cam follower. Just got this motor ,the guy said it started easy and ran good until this year.It has several issues ,he had wrong plugs ,handle has missing parts (on order),water pump etc.I have cleaned carb,changed plugs . It is still hard to start but runs smoothe afterward. Compression is 70 on both cyl.How do I get it to start better.

 

[oldcatamount]

Re: 1990 8 HP Johson J8RESR

The low speed needle should be 1 1/2 turns out (or so) as a starting point. Rarely do you need to go beyond 1 1/2 turns, it's usually less than that. Let the motor run for a few minutes to warm up and turn the needle valve clockwise at 1/8" increments, giving the motor a few seconds to respond. You'll hear (and feel) the motor smooth out when you reach the correct spot.
On the ignition plate, you'll see a hash mark (probably two). That's where the roller is supposed to make contact with the cam (as you turn the throttle handle) at the exact same time as the throttle plate begins to open. If it doesn't, adjust it until it does. Kinda tough to get it right the first try so be patient and do it a couple of times to get it right.

 

[bbx2]

Re: 1990 8 HP Johson J8RESR

So how does this coinside with idle speed screw. Here is what I did ,backed the idle screw all the way off, set the roller as you described then screwed idle speed adjuster screw until it touched. I have not tried to start yet. What do you think. By the way am getting spark to jump 7/16 to 1/2"

 

[oldcatamount]

Re: 1990 8 HP Johson J8RESR

Are we talking about the same things? I'm talking about the low speed needle valve that's on the left side of the carb (near the back) which wouldn't have anything to do with the idle screw (on the outside of the motor, behind the tiller). The low speed needle valve will adjust the rich/lean fuel mixture and (if it's not set right) will make the motor start hard and run rough. The idle screw will simply advance the timing and increase the idle rpm.
Did the cam roller need much adjusting?

 

[the machinist]

Re: 1990 8 HP Johson J8RESR

The reason you see different low speed idle jet settings is because the older metal carb needles had courser threads than most of the plastic topped carbs. The metal ones were almost universally 1 1/2 turns out as a primary setting, while the plastic topped models could be 4 or 5. You may have to do a trial & error, then when running do your fine tuning.

Also to clarify oldcatamount's post, that low speed jet screw also has a coil spring under rthe head to keep it from backing off.

That carb has a low speed throttle adjustment on the middle RH side of the carb that just adjusts the throttle butterfly.

 

[bbx2]

Re: 1990 8 HP Johson J8RESR

The idle adjustment srew on the middle right side and the cam rooer screw just above is the one I am talking about. If I screw the idle adjustment screw down does that not drag the cam roll away from the ingnition plate. By the way I fooled with it some today never got it cranked. Mine is the plastic carb top .Do you think I am getting air , nothing I do seems to help. Thanks you guys and bear with me.

 

[the machinist]

Re: 1990 8 HP Johson J8RESR

You need to set the slow speed adjustment on the right middle first, to an approximate speed you want it to be. Then adjust the left rear idle jet needle, again to where when you screw it in (about 1/8th of a turn at a time) until it sputters & wants to die. Back it off a 1/4 of a turn & you should be good. If you leave it too lean, it will be hard starting, as these motors start on the slow speed jet, not the high speed one.

If you want it slower, then make a slight adjustment in the slow speed screw. Go back & fine tune the idle jet again.

The "link & sync" should have no effect on the idle speed. The adjustment screw on the roller arm is to set this with & in line with the timing plate cam mark.

Your 70# compression seems a tad low, maybe a decarb would help both your low compression & the starting issues.